High‐performance liquid chromatographic enantioseparation of naphthol‐substituted tetrahydroisoquinolines on polysaccharide‐based chiral stationary phases

The stereoisomers of 15 naphthol‐substituted tetrahydroisoquinoline analogs were separated on chiral stationary phases containing the chiral selectors cellulose tris‐(3,5‐dimethylphenyl carbamate) (Cellulose 1), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate) (Cellulose 2), cellulose tris‐(4‐methylbenzoate) (Cellulose 3) and cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate) (Cellulose 4). Experiments were performed in normal‐phase mode with n‐heptane(n‐hexane)–alcohol–diethylamine mobile phases in the temperature range 5–40 °C. Thermodynamic parameters were calculated from plots of lnk or lnα vs 1/T. On the Cellulose 1 column, Δ(ΔH°) ranged from −6.8 to 5.9 kJ/mol, Δ(ΔS°) from −16.7 to 21.0 J/mol/K and the Gibbs energy, −Δ(ΔG°) from 0.2 to 1.5 kJ/mol; on the Cellulose 2 column, Δ(ΔH°) ranged from −7.8 to 2.5 kJ/mol, Δ(ΔS°) from −16.1 to 13.2 J/mol/K and − Δ(ΔG°) from 0.7 to 3.0 kJ/mol. Both enthalpy‐ and entropy‐controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. Copyright © 2013 John Wiley & Sons, Ltd.